Study Of The Pedestal Structure And Predictive Model In H-mode Plasmas

The high-confinement mode(H-mode)regime is currently regarded as a typical operational regime for tokamak devices,and is also considerated to be the most promising scenarios for future tokamak devices.The pedestal is a remarkable feature of H-mode plasmas in the edge barrier region,the pedestal height is associated with total stored plasma energy and strongly impacts tokamak global confinement.Therefore,accurately predicting the pedestal structure is thus essential for understanding and optimizing performance of both present and future tokamaks.Based on the two constraints of the PBM and KBM,the pedestal structure including the width and height can be then completely determined by the EPED model.Through extensive comparisons with experimental data,it has been shown that the EPED model can provide relatively good explanation of the observed pedestal structures in several tokamak devices.Based on the EPED model,we developed the REPED model.The REPED model is essentially the same as the EPED model,with the primary difference being that the equilibrium is calculated using the TEQ equilibrium solver in the CORSICA code,while the TOQ code in the EPED model.The REPED model is used to predict pedestal structures for H-mode plasma discharges in this paper,and compare the predictions with experiments.Firstly,the pedestal width and height are studied for the selected discharges,and try to use the REPED model to predict the pedestal height for type-I ELM H-modes on EAST.It is found that the mean pedestal width ?? correlates with the square root of the poloidal pedestal beta ?p,ped 1/2 and there is very good agreement with??=0.12?p,ped1/2 from experimental observations.This study also shows that the different heating schemes may have no effect on the scaling coefficients of ?? and?p,ped1/2 on EAST.With the pedestal width model,the prediction of pedestal structure is obtained by the REPED model.Besides,we further compare the measured and REPED-predicted pedestal height for the selected discharges;this shows that the REPED model is applicable to predict the pedestal height for a range of experimental pedestal pressures on EAST.Helium(He)or hydrogen(H1)plasmas will be used to test the operationally relevant systems and plasma diagnostics during the non-nuclear phase for ITER.To prepare for ITER operation in these plasmas,H and He experiments have been carried out in present tokamak devices to better understand the behavior of H-mode and ELMs in these plasmas.Here,analyses of pedestal width and height in recent D?-D H-mode experiments in He plasmas finds good agreement with ??=0.095?p,ped1/2between the pedestal width ?? and the square root of the poloidal pedestal beta?p,ped1/2 from experimental observations.The REPED/EPED pedestal model is found to be applicable to predict the pedestal structure of the He plasma from the comparison of predictions with experiments.Furthermore,it indicates that the pedestal height of He and Deuterium(D)plasmas are similar with the same global parameters,and the pedestal width of He plasma is about 7%wider than that of D.CFETR aims to fill the gaps between ITER and DEMO,is in the design stages.The REPED model is applied to predict the pedestal structure for the two operation phases of CFETR.Based on the REPED-predicted pedestal,we construct CFETR equilibria with a self-consistent pedestal structure,using the TEQ code and the Sauter bootstrap current model.These equilibria provide fundamental elements,e.g.plasma geometry,pressure,current and safety factor profiles for other studies,such as the magnetohydrodynamic,transport,heating and current drive.Considering the snowflake(SF)divertor configuration in the CFETR design,we further use the REPED model to compare the pedestal structures of the standard(SD)and SF divertor configuration,and it is shown that the pedestal height of the SF divertor configuration was slightly higher than that of the SD.This also indicates that the SF divertor configuration could reduce the heat flux on the divertor plates,also improve the global confinement for H-mode plasmas.